Illumination optical units of the type mentioned in the introductory part are known from WO 2011/157601 A2 and US 2011/0228247 A1. Further illumination optical units are known from WO 2007/093433 A1 and EP 1 262 836 A1. DE 10 2010 002 822 A1 discloses an illumination system for a microlithographic projection exposure apparatus having a collector unit, a reflective grating and, immediately downstream thereof in the direction of the light, a used-light wavelength selection device having at least one selection mirror. DE 10 2006 047 913 A1 discloses a spectral-analytical unit having a diffraction grating, a camera optical unit, a detector row and evaluation electronics. DE 10 2007 051 520 A1 discloses a spatial light modulator having a grating-based modulator element. US 2002/0079432 A1 discloses a two-dimensional blazed MEMS grating.